1. Field of the Invention
The present invention relates to a spindle motor in which a reduction in thickness has been achieved, and a disk driving apparatus using the same.
2. Description of the Related Art
A disk driving apparatus loaded with an information recording disk like a 3.5-inch floppy disk (hereinafter referred to as a "magnetic disk") is being widely used as an external storage apparatus for a personal computer, word processor or the like, and a reduction in thickness of such a disk driving apparatus is being promoted.
FIG. 23 is a diagram illustrating a spindle motor used in a conventional magnetic disk driving apparatus, and FIG. 24 is an exploded perspective view showing the essential part of FIG. 23.
As shown in these drawings, this spindle motor includes: a spindle shaft 81 fitted into a hole 89 of an oil-retaining metal bush 88 (a first bearing) so as to be rotatably supported therein; a rotor 82; a driving magnet 83 attached to the rotor 82; and driving coils 85 provided on a stator yoke 84, on which a ball bearing 80 (a second bearing section) is placed. The rotor 82 and the spindle shaft 81, which are rotatably supported by the ball bearing 80, are rotated by utilizing a force acting on the rotor 82 due to the current flowing through the driving coils 85 and the magnetic field of the driving magnet 83. Integrally attached to the rotor 82 is a spindle mount 86 having a through-hole into which the spindle shaft 81 is fitted. Numeral 87 indicates an FPC (flexible printed circuit board). The oil-retaining metal bush 88, which has the spindle shaft insertion hole 89, is fastened to the stator yoke 84. The stator yoke 84, the bush 88, etc. form a base unit.
When assembling this spindle motor, the ball bearing 80 is placed on the stator yoke 84, to which the bush 88 is firmly fastened, and the lower end portion of the spindle shaft 81, which is integral with the spindle mount 86 (the rotor 82), is inserted into the hole 89 of the bush 88 protruding from the inner ring of the ball bearing 80.
In the above-described spindle motor for disk driving apparatuses, the spindle mount 86 and the rotor 82 are formed into an integral unit by caulking or gluing prior to the final stage of assembly (i.e., joining this integral unit with the base unit). However, during the insertion of the spindle 81 into the hole 89 of the bush 88, this spindle is under the influence of the strong attracting force of the driving magnet 83, which attracts the rotor 82. Thus, it is rather difficult to insert the spindle shaft 81 into the small-diameter hole 89, this operation being effected by bringing the above integral unit to the base unit held in the horizontal position. Therefore, this operation, which requires a matching jig, etc., has been rather poor in workability. Further, if the rotor yoke 84 and the base unit are assembled together in an inclined position, the inner bore of the hole 89 of the bush 88 will be gouged, resulting in the shaft wobbling, etc., thereby adversely affecting the service life of the disk driving apparatus.